Water-soluble or water-swellable crosslinked copolymers

ABSTRACT

Water-soluble or water-swellable crosslinked copolymers consisting essentially of structural units of the formula 1  
                 
 
     or a mixture of the structural units of the formula 1 with structural units of the formula 2  
                 
 
     and structural units of the formula 3  
                 
 
     where R, R 1 , R 2 , R 3 , Z and n are as defined in the description. These copolymers are crosslinked with compounds which contain at least two olefinic double bonds. These crosslinked copolymers are suitable as thickeners, in particular for cosmetic and pharmaceutical preparations.

FIELD OF THE INVENTION

[0001] The present invention relates to water-soluble or water-swellablecrosslinkable copolymers based on ammonium salts ofacrylamidoalkylsulfonic acids and cyclic

[0002] N-vinylcarboxamides or cyclic and linear N-vinylcarboxamides, tothe preparation thereof and to the use thereof as thickeners,stabilizers of emulsions and dispersions and as glidants in cosmetic andpharmaceutical compositions.

BACKGROUND OF THE INVENTION

[0003] Water- or solvent-containing multicomponent systems, such assolutions, emulsions or suspensions, are frequently adjusted to higherviscosities or thickened for economical or performance reasons, or forstability reasons. Thus, for example, by increasing the viscosity of theexternal or internal phase of emulsions or suspensions, it is possibleto significantly prolong the time before the components of such a systemseparate, which is evident from an extension of the shelf life. For manyproducts, increasing the viscosity also improves their ability to bespread uniformly, in particular on uneven surfaces. This is true inparticular for skincare compositions and pharmaceutical ointments on theskin. In the case of many industrial products, such as wallpaperstripping agents, paint strippers or aircraft de-icers, the increasedviscosity prevents premature run-off from the surface to be treated. Themore uniform distribution and extended contact time thus increase theeffectiveness. As well as the performance advantages mentioned, the highviscosity of such preparations also offers further advantages during thepreparation, packaging, containerizing and storage, as well as duringtransportation, the thickening of acidic media being of particularimportance here from a safety viewpoint. In general, the rheologicalproperties during the preparation and/or formulation of cosmetic,pharmaceutical or industrial preparations are a decisive criterion forthe use of these products in practice. Even when used in extremely smallamounts, the thickeners employed should lead to adequate thickening.However, the color and principal properties of the medium to bethickened should not be changed.

[0004] To adjust the rheological properties of aqueous orsolvent-containing systems, emulsions, suspensions, a large number ofdifferent systems are given in the specialist literature. Known examplesare cellulose ethers and other cellulose derivatives (e.g.carboxymethylcellulose, hydroxyethylcellulose), gelatin, starch andstarch derivatives, sodium alginates, fatty acid polyethylene glycolesters, agar agar, tragacanth or dextrins. The synthetic polymers usedare various materials, such as e.g. polyvinyl alcohols, polyacrylamides,polyacrylic acid and various salts of polyacrylic acid,polyvinylpyrrolidone, polyvinyl methyl ether, polyethylene oxides,copolymers of maleic anhydride and vinyl methyl ether, and variousmixtures and copolymers of the compounds given above.

[0005] However, said compounds exhibit diverse disadvantages upon use.Thus, for example, the cellulose derivatives and, generally, thematerials based on natural raw materials and the formulations resultingtherefrom are very susceptible to bacteria. From an applications-relatedviewpoint, they are mostly noticeable from the formation of unpleasant“stringing” gels. Fatty acid polyethylene glycol esters tend towardhydrolysis in the presence of water, and the insoluble fatty acids whichform in the process cause undesired clouding. Thickeners of naturalorigin (e.g. agar agar or tragacanth) have a composition which variesconsiderably depending on their origin.

[0006] EP-A-0 816 403 and WO 98/00094 describe crosslinked homopolymersof 2-acrylamido-2-methylpropanesulfonates and the use thereof asthickeners. EP-A-0 510 246 describes crosslinked copolymers ofN-vinylcarboxamides and unsaturated alkylamides substituted by asulfonate group, which are likewise suitable as thickeners. U.S. Pat.No. 5,080,809 describes non-crosslinked copolymers of N-vinylpyrrolidoneand 2-acrylamido-2-methylpropanesulfonate. DE 199 05 639.0 describescrosslinked polymers of noncyclic N-vinylcarboxamides andacrylamidoalkylsulfonic acids.

SUMMARY OF THE INVENTION

[0007] Surprisingly, we have now found that alkali metal, alkaline earthmetal or ammonium salts of various acrylamidoalkylsulfonic acids aresufficiently soluble in solvents acceptable for cosmetic applications,such as alcohols or alcohol mixtures, and are therefore highly suitablefor a copolymerization with cyclic N-vinylcarboxamides which arelikewise soluble in these solvents, or mixtures of two or more cyclic

[0008] N-vinylcarboxamides or mixtures of cyclic and linearN-vinylcarboxamides, optionally with further monomers, and monomerswhich act as crosslinkers. In contrast to this, according to the priorart, it is obligatory to work in an aprotic solvent. Since the ammoniumsalt of 2-acrylamido-2-methylpropanesulfonic acid, which is preferablyused for the polymerization, is in ionic form the crosslinked copolymerobtained no longer needs to be subsequently neutralized in an involvedmanner, but can be used as a thickener immediately followingpolymerization and removal of the solvent. A further advantage is thatthrough appropriate choice of the comonomer(s) (cyclic

[0009] N-vinylcarboxamides, mixtures of cyclic and linearN-vinylcarboxamides) it is possible to control the ratio of ionic toneutral building blocks and thus to regulate the thickening action andsalt stability and better match them to specific requirements.Furthermore, as result of the polymerization in alcohol or alcoholmixtures with a water content of less than 10% by weight and here inparticular in tert-butanol, products are obtained which, with regard totheir residual content of solvent remaining in the product, aretoxicologically safe and can thus be used, for example, in cosmeticproducts. The invention provides crosslinked copolymers consistingessentially of

[0010] a1) 1 to 50% by weight of the repeating structural unit of theformula (1)

[0011] where n is an integer from 2 to 9, or

[0012] a2) 1 to 50% by weight of a mixture of the repeating structuralunit of the formula (1) and of the repeating structural unit of theformula (2)

[0013] where R, R¹ and R² may be identical or different and are hydrogenor a linear or branched alkyl or alkenyl group having in each case 1 to30, preferably 1 to 20, in particular 1 to 12, carbon atoms and

[0014] b) 49.99 to 98.99% by weight of the repeating structural unit ofthe formula (3)

[0015] in which R³ is hydrogen, methyl or ethyl, Z is C₁-C₈-alkylene, nis an integer from 2 to 9, and X is an alkali metal or alkaline earthmetal ion, and

[0016] c) 0.01 to 8% by weight, preferably 0.01 to 5% by weight, ofcrosslinking structures resulting from monomers having at least twoolefinic double bonds.

[0017] Preferred copolymers according to the invention contain 2 to 30%by weight, in particular 3 to 15% by weight, of structural units of theformula (1), or (1) and (2), preferably derived from N-vinylpyrrolidone,69.5 to 97.5% by weight, in particular 84.5 to 96.5% by weight, ofstructural units of the formula (3), preferably derived from theammonium salt of 2-acrylamido-2-methylpropanesulfonic acid and 0.2 to 3%by weight, in particular 0.5 to 2% by weight, of crosslinking structuresresulting from monomers having at least two olefinic double bonds. Themixing ratio of the monomers forming the basis of structural units 1 and2 can be varied within any desired limits.

[0018] Crosslinking structures resulting from monomers having at leasttwo olefinic double bonds are preferably derived from allyl acrylate orallyl methacrylate, dipropylene glycol diallyl ether, polyglycol diallylether, triethylene glycol divinyl ether, hydroquinone diallyl ether,tetraallyloxyethane or other allyl or vinyl ethers of multifunctionalalcohols, tetraethylene glycol diacrylate, triallylamine,trimethylolpropane diallyl ether, methylene bisacrylamide ordivinylbenzene. The crosslinking structures are particularly preferablyderived from monomers of the formula (4),

[0019] in which R is hydrogen, methyl or ethyl.

[0020] The copolymers according to the invention are prepared bydissolving or dispersing the monomers corresponding to the repeatingstructural units of the formulae (1), (2) and (3) in a protic solvent,adding one or more crosslinkers having at least two olefinic doublebonds to this solution or dispersion, and starting the polymerization ina manner known per se by adding a free-radical- forming compound.

[0021] Preference is given to copolymerizing the ammonium salt ofacrylamidopropanesulfonic acid. Instead of this ammonium salt, it isalso possible to use the free acrylamidopropanesulfonic acid and, beforeadding the remaining monomers, producing the ammonium salt from the freeacid by introducing ammonia.

[0022] The polymerization reaction is preferably carried out in awater-soluble alcohol or a mixture of two or more alcohols having 1 to 6carbon atoms, preferably in tert-butanol. The water content of thealcohol or of the mixture of two or more alcohols must not exceed 10% byweight since otherwise the formation of lumps can occur over the courseof the polymerization. Specifically, the type and amount of solvent arechosen such that the salt of acrylamidoalkylsulfonic acid of the formula1, in particular of 2-acrylamido-2-methylpropanesulfonic acid, islargely soluble or dispersible therein. Largely soluble or dispersibleis understood as meaning that even after the stirrer has been switchedoff, no solid material settles out of the solution or dispersion. Bycontrast, the polymer formed in the course of the reaction should belargely insoluble in the chosen solvent (or solvent mixture). Largelyinsoluble is understood here as meaning that in the course of thepolymerization a readily stirrable pulpy polymer paste is produced inwhich no lumps or agglutinations must form. The filtrate which isobtainable by filtering the paste with suction must have a solidscontent of at most 5% by weight. If the copolymers are soluble in thechosen solvent or solvent mixture to a greater extent, clumping mayresult during drying of the polymer paste. The polymerization reactionitself is triggered in a manner known per se by free-radical-formingcompounds, such as azo initiators (e.g. azobisisobutyronitrile),peroxides (e.g. dilauryl peroxide) or persulfates in a suitabletemperature range from 20 to 120° C., preferably between 40 and 80° C.,and is continued over a period of from 30 min to several hours.

[0023] The copolymer composition can be varied by varying theabove-described ratio of the monomers used, and the proportion ofcrosslinker and thus be used to achieve a tailored profile ofproperties. For example, by incorporating more ammonium salts ofacrylamidosulfonic acids, it is possible to improve the thickeningaction of the polymers, while by incorporating more cyclicN-vinylcarboxamide, it is possible to improve the electrolytecompatibility of the polymers and the solubility thereof in nonaqueoussystems. In contrast to polymers based on acrylic acid which, in theneutral or slightly alkaline range in 1% strength aqueous solution,exhibit viscosities of more than 30 000 mPa s, but whose thickeningability (or the measured viscosity) deteriorates considerably withdecreasing pH, the copolymers described according to the invention areable to maintain their viscosity up to an acidic pH of about 3.

EXAMPLES Example 1

[0024] A 1000 ml flask fitted with anchor stirrer, reflux condenser,internal thermometer, feed option for N₂ and NH₃ was charged with 490.5g of tert-butanol and 11.5 g of water. 80.75 g of2-acrylamido-2-methylpropanesulfonic acid were then introduced anddispersed with vigorous stirring, clouding of the solvent beingretained. Over a period of 30 min, 6.64 g of ammonia were introducedinto the overhead gas space and the mixture was stirred for at least afurther 30 min until a pH of 6-7 had been established. 4.10 g ofN-vinylpyrrolidone and 0.8 g of allyl methacrylate were added, and thereceiver was rinsed in each case with tert-butanol (about 6 ml) in orderto minimize losses during the addition. The reaction mixture was thenheated to a temperature of T=60° C., the reaction mixture being renderedinert by the simultaneous introduction of N₂. After the temperature ofT=60° C. had been reached, 1.0 g of dilauryl peroxide was added. Thereaction started immediately after the initiator had been added, beingrecognizable from an increase in the temperature and from flocculationof the polymer. Approximately 15 minutes after the polymerizationreaction had started, the nitrogen feed was switched off. Approximately30 minutes after the initiator dilauryl peroxide had been added, thetemperature reached a maximum (about 65-70° C.). For a further 30minutes after this maximum had been passed, the mixture was heated toreflux and then stirred under these conditions for two hours. Thecontents of the reaction vessel developed a pulp-like consistency overthe course of the reaction, but was still readily stirrable. The mixturewas then cooled to room temperature and the solid was filtered off withsuction. The paste was dried at 60-70° C. in a vacuum drying cabinet for24 hours, giving 92.2 g of a fine white powder.

Example 2

[0025] Example 1 was repeated except that instead of allyl methacrylateas crosslinker, 1.65 g of trimethylolpropane methacrylate were used.

Example 3

[0026] In accordance with Example 1, the crosslinked copolymer wasprepared from 35 g of 2-acrylamido-2-methylpropanesulfonic acid, 55 g ofN-vinylpyrrolidone and 1.9 g of trimethylolpropane triacrylate.

Example 4

[0027] In accordance with Example 1, the crosslinked copolymer wasprepared from 77.5 g of 2-acrylamido-2-methylpropanesulfonic acid, 8.9 gof N-vinylpyrrolidone, 4.2 g of N-vinylformamide and 1.8 g oftrimethylolpropane triacrylate.

Comparative Example 1

[0028] In accordance with Example 1, a crosslinked homopolymer wasprepared from 85 g of 2-acrylamido-2-methylpropanesulfonic acid and 0.8g of allyl methacrylate.

[0029] Test Results:

[0030] The powders obtained according to the examples were in each casedissolved in an amount of 1.0% by weight in distilled water, and theviscosity of the gels thereby formed was measured at 25° C. For this, 5g of dried polymer powder were in each case stirred into 495 g ofdistilled water in a 600 ml beaker, and the viscosity of the gel therebyformed was measured using a Brookfield RVT type viscometer at 20 rpm.The gels prepared in this way are particularly suitable for cosmeticapplications since they impart a pleasant feel to the skin when spreadon the body.

[0031] The acid stability was likewise determined by measuring theviscosity using the Brookfield viscometer. For this, the copolymerprepared as in Preparation Example 1 was compared with a commerciallyavailable polymer based on acrylic acid (Carbopol® 934 from Goodrich).1.0% strength gels of both polymers were prepared according to themethod described above, their pH being adjusted, where appropriate to anacidic value (pH =about 3) and to a neutral value (pH=6-7) by addingNaOH and H₃PO₄, respectively. TABLE Measured viscosities of the 1.0%strength gels pH Polymer from Example 1 Carbopol 934 6-7 65 600 mPa · s76 600 mPa · s about 3 52 100 mPa · s   140 mPa · s

[0032] As the table shows, in contrast to the polymers constructed onthe basis of acrylic acid, the polymers described according to theinvention exhibit very good thickening properties even at an acidic pH.

[0033] The copolymers according to the invention are notable for theirgood thickening action, in particular in cosmetic and pharmaceuticalpreparations at concentrations of solid copolymer of from 0.1 to 5% byweight, preferably of from 2 to 0.5% by weight, particularly preferablyof from 0.7 to 1% by weight, based on the finished composition. At roomtemperature in deionized water and at a pH of 6 to 7, viscosities ofmore than 60000 mPas are achieved.

[0034] The copolymers according to the invention exhibit only relativelyslight changes in viscosity over a broad pH range, in particular in arange from pH 2.5 to 7. Furthermore, they retain their good solubilityin water in the formulations and can be readily washed off from theskin. Their thickening and stabilizing properties are also effective inaqueous, alcoholic and/or glycol-containing solutions. They are UVstable and are stable over a wide temperature range from 0 to 50° C.

[0035] By varying the monomers acrylamidosulfonic acid salt andN-vinylcarboxamide, and the proportion of crosslinker, copolymers areobtained which can be used as thickeners both in oil-in-water emulsions,and in water-in-oil emulsions at a pH of from 7 to 2.5. Irrespective ofwhether the intention is to prepare lotions with a comparatively lowviscosity, or creams and ointments with high viscosities, emulsionscomprise an oil substance consisting essentially of emulsifier(s) and anoil phase in the amounts by weight of from 5 to 95%, preferably 25 to85%, and water to make up 100% by weight. Suitable oil substances arevegetable, animal, mineral and synthetic oils, for example Guerbetalcohols having 6 to 18, preferably 8 to 10, carbon atoms, esters oflinear C₆-C₁₃-fatty acids with linear C₆-C₂₀-fatty alcohols, esters ofbranched C₆-C₁₃-carboxylic acids with linear C₆-C₂₀-fatty alcohols,esters of linear C₆-C₁₈-fatty acids with branched alcohols, inparticular 2-ethylhexanol, esters of linear and/or branched fatty acidswith polyhydric alcohols (such as e.g. dimerdiol or trimertriol) and/orGuerbet alcohols, triglycerides based on C₆-C₁₀-fatty acids, vegetableoils, branched primary alcohols, substituted cyclohexanes, Guerbetcarbonates, dialkyl ethers and/or aliphatic or aromatic hydrocarbons.

[0036] The emulsions may be in the form of skincare compositions, suchas, for example, day creams, night creams, care creams, nourishingcream, body lotions, ointments and the like, and may comprise, asfurther auxiliaries and additives, coemulsifiers, superfatting agents,fats, waxes, stabilizers, biogenic active ingredients, glycerol,preservatives, pearlizing agents, dyes and fragrances.

[0037] Superfatting agents which may be used are substances such as, forexample, polyethoxylated lanolin derivatives, lecithin derivatives,polyol fatty acid esters, monoglycerides and fatty acid alkanolamides,the latter also serving as foam stabilizers. Typical examples of fatsare glycerides, and suitable waxes are, inter alia, beeswax, paraffinwax or microcrystalline waxes, optionally in combination withhydrophilic waxes, e.g. cetylstearyl alcohol.

[0038] Stabilizers which may be used are metal salts of fatty acids,such as e.g. magnesium stearate, aluminum stearate and/or zinc stearate.Biogenic active ingredients are understood as meaning, for example,plant extracts and vitamin complexes.

[0039] Suitable preservatives are, for example, phenoxyethanol,formaldehyde solution, parabens, pentanediol or sorbic acid.

[0040] Suitable pearlizing agents are, for example, glycol distearicesters, such as ethylene glycol distearate, but also fatty acidmonoglycol esters. Dyes which may be used are the substances approvedand suitable for cosmetic purposes, as listed, for example, in thepublication “Kosmetische Farbemittel” [Cosmetic Colorants] from theFarbstoffkommission der Deutschen Forschungsgemeinschaft [DyesCommission of the German Research Society], Verlag Chemie, Weinheim,1984, pp. 81-106.

[0041] The total amount of auxiliaries and additives can be 1 to 10% byweight, preferably 2 to 5% by weight, based on the composition. Thecompositions can be prepared in a manner known per se, i.e. for exampleby hot, hot-hot/cold or PIT emulsification.

[0042] The examples below serve to illustrate the applicationpossibilities of the thickeners according to the invention, withoutlimiting them thereto. The percentages are percentages by weight in allcases. EXAMPLE 1 O/W cream A Hostacerin DGI 2.00% Mineral oil, lowviscosity 8.00% Isopropyl palmitate 4.00% Eutanol G 4.00% B Copolymer 11.20% C Hostapon KCG 0.80% Water ad 100% Preservative q.s. D Fragrances0.40%

[0043] Method of Preparation

[0044] I Stir B into A, then add C and stir well

[0045] II Stir D into I

[0046] III Homogenize EXAMPLE 2 O/W skin milk A Hostacerin DGMS 2.00%Mineral oil, high viscosity 8.00% Isopropyl palmitate 5.00% Cetiol 8684.00% B Copolymer 2 0.50% C Hostapon KCG 2.00% Glycerol 4.00% Water ad100% Preservative q.s. D Fragrances 0.30%

[0047] Method of Preparation:

[0048] I Melt A to about 70° C.; add B

[0049] II Heat C to about 70° C.

[0050] III Stir II into I and stir until cool

[0051] IV Add D at about 35° C.

[0052] V Homogenize EXAMPLE 3 O/W skin milk A Hostacerin DCL 2.00%Isopropyl palmitate 4.00% Almond oil 5.00% Wheatgerm oil 1.00% Cetiol SN8.00% B Copolymer 1 0.60% C Water ad 100% Preservative q.s. D Fragrances0.30%

[0053] Method of Preparation:

[0054] I Mix A and B and stir into C

[0055] II Add D

[0056] III Homogenize EXAMPLE 4 O/W skin milk A Hostaphat CG 120 1.50%Mineral oil, low viscosity 5.00% Miglyol 812 4.00% Isopropyl palmitate6.00% Soybean oil 3.00% Jojoba oil 2.00% B Copolymer 1 0.80% C HostaponKCG 1.00% Water  100% Glycerol 3.00% Soda (10% in water) 1.20%Preservative q.s. D Fragrances 0.30%

[0057] Method of Preparation:

[0058] I Stir B into A, add C thereto and mix well

[0059] II Add D

[0060] III homogenize Commercial products ®Hostacerin DGI (ClariantGmbH) Polyglyceryl-2 sesquiisostearate ®Eutanol G (Henkel KGaA)Octyldodecanol Copolymer 1 Copolymer as in Example 1 Copolymer 2Copolymer as in Example 2 ®Hostapon KCG (Clariant GmbH) Sodium cocoylglutamate Hostacerin DGMS (Clariant GmbH) Polyglyceryl-2 stearate®Cetiol 868 (Henkel KGaA) Octyl stearate Hostacerin DGL (Clariant GmbH)Polyglyceryl-2 PEG-10 laurate ®Cetiol SN (Henkel KGaA) Cetearylisononate ®Hostaphat CG 120 (Clariant GmbH) Octyldecyl phosphate®Miglyol 812 (Dynamit Nobel AG) Capryl triglyceride

1. A water-soluble or water-swellable crosslinked copolymer consistingessentially of a1) 1 to 50% by weight of the repeating structural unitof the formula (1)

where n is an integer from 2 to 9, or a2) 1 to 50% by weight of amixture of the repeating structural unit of the formula (1) and of therepeating structural unit of the formula (2)

where R, R¹ and R² may be identical or different and are hydrogen or alinear or branched alkyl or alkenyl group having in each case 1 to 30,preferably 1 to 20, in particular 1 to 12, carbon atoms and b) 49.99 to98.99% by weight of the repeating structural unit of the formula (3)

in which R³ is hydrogen, methyl or ethyl, Z is C₁-C₈-alkylene, n is aninteger from 2 to 9, and X is an alkali metal or alkaline earth metalion, and c) 0.01 to 8% by weight of crosslinking structures resultingfrom monomers having at least two olefinic double bonds.
 2. Thecopolymer as claimed in claim 1 , consisting essentially of 2 to 30% byweight of the repeating structural unit of the formula 1 or a mixture ofthe repeating structural units of the formulae 1 and 2, 69.5 to 97.5% byweight of the repeating structural unit of the formula 3 and 0.2 to 3%by weight of crosslinking structures resulting from monomers having atleast two olefinic double bonds.
 3. The copolymer as claimed in claim 1, consisting essentially of 3 to 15% by weight of the repeatingstructural unit of the formula 1 or a mixture of the repeatingstructural units of the formulae 1 and 2, 84.5 to 96.5% by weight of therepeating structural unit of the formula 3 and 0.5 to 2% by weight ofcrosslinking structures resulting from monomers having at least twoolefinic double bonds.
 4. The copolymer as claimed in claim 1 ,comprising crosslinking structures resulting from allyl (meth)acrylate.5. A process for the preparation of the water-soluble or water-swellablecopolymers as claimed in claim 1 , which comprises dissolving ordispersing the monomers corresponding to the repeating structural unitsof the formulae 1, 2 and 3 in a protic solvent, adding one or morecrosslinkers having at least two olefinic double bonds to this solutionor dispersion, and starting the polymerization by adding afree-radical-forming compound.
 6. The use of the water-soluble orwater-swellable copolymers as claimed in claim 1 as thickeners.
 7. Acosmetic or pharmaceutical preparation comprising a water-soluble orwater-swellable copolymer as claimed in claim 1 .